Removal of arterial obstructions formed by obstructive material in arteries and blood vessels has been made possible due to advances in medical treatment technology, and there are various methods currently employed. One such method involves introducing a flexible catheter into the cardiovascular system of a patient. The flexible catheter has a rotatable torque tube disposed in the lumen of the catheter, and the torque tube has a cutting apparatus attached to one end thereof for excising obstructive tissue from the artery. The flexible catheter and rotatable torque tube are introduced and steered along the blood vessel to the point of the obstruction. The rotary cutter can then be used to excise the obstructive tissue from the vessel. Specifically, the cutting apparatus has blades which are driven by the rotatable torque tube to excise obstructive tissue from the lumen of the blood vessel. To do this, the torque tube must be of sufficiently small size to fit into the artery of the patient and be able to be passed along the lumen of the vessel to the point of the obstruction. In addition, the torque tube must be flexible enough to accommodate the various bends and turns encountered in the vessel through which it must pass. The torque tube must be of sufficient stiffness, however, to be able to transmit torque from one end of the torque tube which is attached to the drive mechanism, to the other end of the torque tube which is attached to the cutting head. In addition, the torsional rigidity required must be firm enough to respond adequately to changes in the angular velocity of the drive mechanism so that the cutting head is responsive to changes in the rotational drive speed. Furthermore, in order to reduce the overall size of the cutting apparatus, it is desirable that the torque tube have a maximum inner diameter and minimum outer diameter, i.e. minimum acceptable wall thickness. It is also desirable that the torque tube be manufactured accurately within close tolerances.
Several methods have been proposed for manufacturing catheters for insertion into the cardiovascular system. They are not, however, necessarily utilized as torque tubes. For example, U.S. Pat. No. 4,516,972 to Samson discloses a guiding catheter and method of manufacture. A helically-wound ribbon of flexible material is embedded in the wall of the catheter to provide torsional rigidity and the stiffness of the catheter is controlled by varying the pitch of the helically-wound ribbon. In manufacturing the catheter, the catheter is covered with an outer jacket of flexible material fabricated of a thermal plastic material, such as polyethylene or heat-shrinkable tubing. In addition, the Samson patent discloses means for obtaining variations in torsional rigidity and stiffness by changing the pitch or density of the helical winding of the ribbon about the liner tube. The outer jacket comprises a length of heat-shrinkable tubing placed over the ribbon and heated to shrink fit. Unfortunately, there is no provision for monitoring or maintaining the accuracy of the outer diameter, nor for allowing appropriate adjustments to be made during its manufacture.
The present invention thus recognizes the need for a system for manufacturing torque tubes which provides desired flexibility and stiffness in various portions of the tube, yet maintains overall accuracy of the outside diameter. In addition, the present invention recognizes that rotating a liner tube at a specific angular velocity, in combination with the translational velocity of the wire being wound onto the liner tube, may determine the proper pitch and separation of the wire. In addition, the present invention recognizes that an outer layer may be applied onto the tube with required precision.
Accordingly, it is an object of the present invention to provide a method and apparatus for manufacture of torque tubes which provide desired torsional rigidity and flexibility to accommodate the needs of a particular patient undergoing an atherectomy procedure. It is a further object of the present invention to provide an apparatus and method for manufacturing a torque tube in which the outside diameter of the torque tube may be accurately maintained within desired tolerance limits. It is a further object of the present invention to provide a method and apparatus for manufacturing a torque tube which has minimal wall thickness and yet provides required flexibility and torsional rigidity for a given patient. It is yet another object of the present invention to provide a method and apparatus for manufacturing torque tubes in which the user may select various parameters for its construction, such as the pitch of the wire windings and the outside diameter, which parameters vary along the length of the tube to accommodate the path within a vessel. It is yet another object of the present invention to provide a method and apparatus for manufacturing torque tubes which is durable in construction and reliable and cost-effective in its manufacture and use. It is yet another object of the present invention to provide a method and apparatus for manufacturing torque tubes which is simple and convenient to use.